An extinction‐emergency metacollection: Maximising future recovery options for Rhodomyrtus psidioides (Myrtaceae), threatened by Myrtle Rust

Abstract

A challenge for wild plant conservation is the rising incidence of plant pathogens that are difficult to interdict, contain and manage. Invasive, fast‐moving, broad‐spectrum pathogens impose societal costs through losses of intrinsically valuable wild biodiversity, ecosystem function, current and potential genetic and biological assets, culturally significant species and public confidence in biosecurity and biodiversity management. In response to one pathogen causing catastrophic decline in wild species, Australian teams are conducting emergency germplasm capture and establishing representative ex situ metacollections to enable resistance breeding. Our pilot model integrates consideration of resourcing, information and genetic management, human systems and phytosanitary factors. Native Guava ( Rhodomyrtus psidioides ), a formerly common small‐tree species of mesic forests, is one of numerous endemic east‐Australian taxa in the family Myrtaceae known to be undergoing catastrophic decline and reproductive failure in the wild, as a direct result of Myrtle Rust disease caused by the introduced fungal pathogen Austropuccinia psidii . Many of these species, including Native Guava, are exposed to the disease over the totality of their distribution. No remedial management options currently exist for use at scale in wild populations. Extinction of Native Guava in the wild is likely within one plant generation. In 2019, a framework for collecting and securing genetically representative germplasm was established to keep open the possibility of recovery through ex situ breeding for rust tolerance traits and eventual re‐wilding. Here, we outline the process of establishing a comprehensive multi‐partner metacollection to propagate and maintain multiple wild genotypes as a pilot and proof‐of‐concept first stage towards that recovery goal. We consider risk analysis, procedures, training, funding, germplasm capture strategy, propagation, collection optimisation and dispersal, and ongoing monitoring and maintenance requirements. This model, although still under development, can be applied to other species in rapid decline due to Myrtle Rust and to at least some other species under similar whole‐of‐range and fast‐acting existential threats.